Supporting basket for an end winding

ABSTRACT

A supporting basket for an end winding of a stator winding of an electrical machine, the supporting basket including: at least one supporting ring; a plurality of supporting brackets arranged circumferentially distributed along the at least one supporting ring and attached to the at least one supporting ring; and a plurality of round connectors arranged radially externally on the supporting brackets, the round connectors extending circumferentially and being attached to the supporting brackets; wherein the supporting brackets, the at least one supporting ring, and the round connectors comprise an impregnation formed by dip-impregnation as a preassembled unit.

This application is a Divisional of, and claims priority under 35 U.S.C.§120, to U.S. patent application Ser. No. 12/610,428, filed 2 Nov. 2009now U.S. Pat. No. 8,074,343, which was a Continuation of, and claimedpriority under 35 U.S.C. §120 to, International application no.PCT/EP2008/054734, filed 18 Apr. 2008, and claimed priority therethroughunder 35 U.S.C. §§119, 365 to Swiss application no. No. 00751/07, filed9 May 2007, the entireties of which are incorporated by referenceherein.

BACKGROUND

1. Field of Endeavor

The present invention relates to a method for production of a supportingbasket with round connectors for an end winding of a stator winding ofan electrical machine, and also relates to a supporting basket havinground connectors for an end winding of a stator winding of an electricalmachine.

2. Brief Description of the Related Art

Large electrical machines such as generators and electric motors whichare used in power stations have a stator with an electrical statorwinding. This stator winding is passed out of the stator, at least atone axial end of the stator, where it forms an end winding. An endwinding such as this is formed in particular by end sections ofconductors, which are in the form of bars, of the stator winding, whichare angled in the radial direction and in the circumferential directionsuch that the end winding is in the form of a truncated cone, whichwidens as the distance from the associated end-face stator endincreases. A supporting basket is normally provided in order to supportthe end winding. This supporting basket may have a plurality ofsupporting brackets which are distributed in the circumferentialdirection and are arranged radially externally on the end winding. Anaxial support for the end winding can be provided, for example, viathese supporting brackets at the associated front-side end of thestator. A supporting basket such as this normally has one or twosupporting rings, which extend in the circumferential direction and towhich the supporting brackets are attached. In this case, the supportingrings can support the supporting brackets radially, and thus allow themto absorb radial supporting forces.

In order to allow the stator winding to be electrically connected to anelectrical system, for receiving the current produced by a generatorand/or for providing the current required by an electric motor, thewinding bar sections of the end winding are electrically connected attheir bar ends, in a complex, predetermined manner, to a plurality ofso-called round connectors, which themselves form electrical connectionsto the end winding. The stator winding can be connected to theelectrical system via these connections, which are formed with the aidof the round connectors. The round connectors which are used in thiscase must be electrically insulated and must also be impregnated, inorder to prevent the ingress of moisture.

In principle, it is possible to insulate the round connectors wet or dryas individual parts, for the production of the end winding.Wet-insulated round connectors are likewise dried and cured asindividual parts. Wet insulated ground connectors in principle do notrequire any impregnation. In contrast to this, dry-insulated roundconnectors must additionally be impregnated. To do this, it is inprinciple possible to impregnate the dry-insulated round connectorsindividually and then to dry and cure them. An appropriate impregnationtool can be used for this purpose. In the case of long round connectors,it may be necessary to mechanically separate them before dry insulation,then to impregnate them and only then to join them together again, forexample by welded joints or soldered joints. The weld or solder pointsmust then be locally wet-insulated and dried, and cured.

For fitting of the end winding, it is also necessary to fit thesupporting basket to the respective stator end, that is to say, to fitthe supporting brackets and the supporting rings to the stator end. Thecompletely insulated, and possibly impregnated, round connectors canthen be fitted to the supporting basket, using appropriate attachmentdevices for this purpose. When the round connectors are being fitted,they can be moved along the supporting brackets. In order to preventdamage to the insulation and impregnation during this process, wetcushions can be used here. After the round connectors have been fitted,the attachment devices that are used are also locally wet-impregnated.The associated drying and curing of these local impregnation points canbe carried out, for example, in the course of a heat treatment of thestator. Overall, a production process such as this is comparativelycomplex.

SUMMARY

One of numerous aspects of the present invention deals with the problemof an improved embodiment for a production method of the aforementionedtype and for a supporting basket having round connectors of the typementioned initially, which embodiment is distinguished in particular bythe capability to produce the end winding and the supporting basketeasily.

Another aspect includes the general idea of first of all constructingthe supporting basket independently of the stator, with supportingbrackets, at least one supporting ring and all the round connectors, inorder subsequently to impregnate a completely preassembled unit. Theimpregnation is in this case carried out by immersion in an impregnationagent bath and by evacuation of the impregnation agent bath. Thisresults in high-quality impregnation which, in particular, avoids airenclosures in concealed areas. One particularly advantageous aspect ofthe proposed procedure is that a completely impregnated preassembledunit is created which can be fitted as such to the stator without havingto carry out any further relative movements between the supportingbrackets and the tubular connectors. The risk of damage to theimpregnation and/or insulation as a result of relative movements betweenthe supporting brackets and the round connectors can thus be reducedconsiderably.

A further advantage is that the respectively used attachment devices, bywhich the round connectors are attached to the supporting brackets,likewise form a component of the preassembled unit and are thereforealso impregnated. This makes it possible to improve the robustness andstiffness of the supporting basket. This avoids the need forcorresponding subsequent treatment by local wet impregnation. This isparticularly advantageous with regard to the health of the fitters sincethey are not confronted with vapors from the wet impregnation agent.

Further important features and advantages of the present invention willbecome evident from the drawings and from the associated description ofthe figures on the basis of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are illustrated in the drawingsand will be explained in more detail in the following description, inwhich the same reference symbols relate to the same, similar orfunctionally identical components. In the figures, in each caseschematically:

FIG. 1 shows an axially sectioned view of a supporting basket with roundconnectors in an impregnation bath,

FIG. 2 shows a plan view of the supporting basket with round connectorsin the impregnation bath, corresponding to a viewing direction II inFIG. 1,

FIG. 3 shows a section view corresponding to the section lines III inFIG. 2,

FIG. 4 shows a view as in FIG. 1, but of a different embodiment,

FIG. 5 shows a plan view of the arrangement shown in FIG. 4,corresponding to a viewing direction V in FIG. 4,

FIG. 6 shows a section view corresponding to the section lines VI inFIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As shown in FIGS. 1 to 6, a supporting basket 1 has a plurality ofsupporting brackets 2 which are arranged distributed in thecircumferential direction with respect to a longitudinal center axis 3of the supporting basket 1. Furthermore, the supporting basket 1 has atleast one supporting ring 4 or 5. The embodiment shown in FIGS. 1 to 3has two supporting rings 4, 5, while the embodiment shown in FIGS. 4 to6 has only one supporting ring 4. The supporting brackets 2 are attachedto the respective supporting ring 4, 5.

Furthermore, a plurality of round connectors 6 are attached to thesupporting basket 1. These are arranged on the supporting brackets 2,radially on the outside with respect to the longitudinal center axis 3,and extend in the circumferential direction. Furthermore, the roundconnectors 6 are attached to the supporting brackets 2. In the exemplaryembodiments shown here, strings 7 are used as attachment devices, andare preferably in the form of glass strings. Furthermore, the roundconnectors 6 are expediently insulated. Appropriate electricalinsulation can be seen in the enlarged illustration in FIG. 3 and FIG. 6and is annotated 8.

In the embodiment shown in FIGS. 1 to 3, the round connectors 6 have ahollow profile, by way of example. In addition, by way of example here,they have a round cross section, in particular a circular cross section.In contrast to this, the round connectors 6 in the embodiment shown inFIGS. 4 to 6 have a solid profile and, by way of example, have arectangular cross section. Other cross-sectional profiles are likewisefeasible, for example a square cross section. The round connectors 6with a rectangular profile can likewise be hollow. The round connectors6 with a round or circular cross section can also likewise have a solidprofile.

The supporting basket 1 is used for fitting to a stator of an electricalmachine, which is preferably a generator. However, it may also inprinciple be an electric motor. The stator has a stator winding which ispassed out of the stator at at least one axial end of the stator, whereit forms an end winding. This end winding must be supported. Thesupporting basket 1 is used for this purpose. The end winding is in thiscase conventionally formed by winding bar end sections which projectaxially out of the axial end of the stator, where they are bent outwardsin the radial direction and in the circumferential direction, in orderto form a truncated conical assembly there, whose cross section widensas the distance from the stator end increases. The end winding formed inthis way is then supported radially on the outside by the supportingbasket. In the fitted state, and depending on the embodiment, an axialsupport can also be provided for the end winding on the stator end withthe aid of the supporting basket 1. In particular, in this case, thesupporting brackets 2 can be supported axially on the stator end.Furthermore, radial forces can be absorbed via the supporting rings 4,5. Depending on the embodiment of the round connectors 6, these canlikewise absorb forces radially, and can thus contribute to making thesupporting basket 1 more robust.

With regard to the fitting position on the stator, the supporting basketshown in FIGS. 1 to 3 has a supporting ring 4 which is located axiallyon the outside, that is to say an outer supporting ring 4, and asupporting ring 5 which is located axially on the inside, that is to sayan inner supporting ring 5. The outer supporting ring 4 engages radiallyover the supporting brackets 2, thus allowing them to be supportedthereon in the radial direction. In contrast to this, the embodiment ofthe supporting basket 1 illustrated in FIGS. 4 to 6 has only one outersupporting ring 4, which is located axially on the outside. This is inthis case fitted axially to the supporting brackets 2. The roundconnectors 6 are used to electrically connect the winding bar endsections in a predetermined manner, in order in this way to formelectrical connections 9. For this purpose, the round connectors 6 areconnected in a suitable manner to the bar ends of the winding barsections. By way of example, appropriate connecting pieces can be seenin FIG. 5, and are annotated 10.

The supporting basket 1 is preferably produced as follows:

First of all, the round connectors 6 are insulated. This is preferablydone using dry insulation. By way of example, insulation strips whichwork using mica as the insulation material, so-called mica insulationstrips, are suitable for dry insulation.

The supporting brackets 2 are arranged distributed over thecircumference independently of the insulation 8 on the round connectors6, and are firmly connected to one supporting ring 4 or to bothsupporting rings 4, 5. This results in a framework to which theinsulated round connectors 6 can be fitted. This is then the next step.The insulated round connectors 6 are fitted to the framework, which isheld together by the at least one supporting ring 4, 5 and is composedof the supporting brackets 2. In this case, the round connectors 6 areattached to the supporting brackets 2, preferably using the strings 7that are shown here. Furthermore, the round connector ends can also beattached to one another, for example in order to form the connections 9.

If the round connectors 6 have hollow profiles, the open ends must beappropriately sealed, for example by suitable plugs. If the supportingbasket 1 has mechanical interfaces which do not need to be impregnated,then these can be covered with an appropriate coating. As can also beseen from FIG. 6, the round connectors 6 can be supported via specialcushions 11 on the supporting brackets 2. This makes it possible toreduce the load on the round connectors 6.

The supporting basket 1 which has been prepared in this way and has beencompletely assembled from the mechanical point of view, can then beimmersed in an impregnation agent bath 12, which is accommodated in anappropriate pool 13.

In order now to make it possible to wet all of the insulation 8 andstrings 7 on the supporting basket 1, to be impregnated as completely aspossible with the impregnation agent, the impregnation agent bath 12 isadditionally evacuated. By way of example, the pool 13 is for thispurpose closed by a cover, which is not shown here, and is connected toan appropriate vacuum-pressure source. Air enclosures are thus removed,thus making it possible to achieve the desired homogeneous wetting.

After the evacuation process, the supporting basket 1, which has beenimpregnated to this extent, is then removed from the impregnation agentbath 12 and is passed to a drying process or a curing process. By way ofexample, the drying or curing of the impregnation agent is carried outin an appropriate oven.

Once the impregnation agent has been cured, the supporting basket 1 iscomplete. It is characterized in particular in that its round connectors6 are dip-impregnated in the assembled state, that is to say with thesupporting brackets 2 and the corresponding attachment devices.

The complete supporting basket 1 can be fitted to the stator, once theimpregnation has cured. The end winding can then be fitted during thewinding of the stator, and can be electrically connected to the roundconnectors 6.

In the assembled state, the longitudinal center axis 3 of the supportingbasket 1 then coincides with a rotation axis of a rotor of theelectrical machine.

LIST OF REFERENCE SYMBOLS

1 Supporting basket

2 Supporting bracket

3 Longitudinal center axis

4 Outer supporting ring

5 Inner supporting ring

6 Round connector

7 String

8 Insulation

9 Connection

10 Connecting piece

11 Cushion

12 Impregnation agent bath

13 Pool

While the invention has been described in detail with reference toexemplary embodiments thereof, it will be apparent to one skilled in theart that various changes can be made, and equivalents employed, withoutdeparting from the scope of the invention. The foregoing description ofthe preferred embodiments of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Theembodiments were chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto, and theirequivalents. The entirety of each of the aforementioned documents isincorporated by reference herein.

We claim:
 1. A supporting basket for an end winding of a stator windingof an electrical machine, the supporting basket comprising: at least onesupporting ring; a plurality of supporting brackets arrangedcircumferentially and distributed along the at least one supporting ringand attached to the at least one supporting ring; and a plurality ofround connectors arranged external to the supporting brackets in theradial direction of the at least one supporting ring, the roundconnectors extending circumferentially and being attached to thesupporting brackets; wherein the supporting brackets, the at least onesupporting ring, and the round connectors are impregnated by animpregnation agent as a preassembled unit, and the plurality of roundconnectors are supported via cushions on the supporting brackets.
 2. Thesupporting basket as claimed in claim 1, further comprising: glassstrings attaching the round connectors to the supporting brackets. 3.The supporting basket as claimed in claim 1, further comprising:electrical insulation on the round connectors.
 4. The supporting basketas claimed in claim 1, wherein the round connectors have a solid profileor a hollow profile.
 5. The supporting basket as claimed in claim 1,wherein the round connectors have a round, circular, rectangular, orsquare cross section.
 6. The supporting basket as claimed in claim 1,wherein a supporting ring of the at least one supporting ring radiallyextends beyond outer surfaces of the plurality of supporting brackets.